Field of the Invention
The present invention relates to a method of manufacturing, for example, a high aspect ratio structure such as an ultrasonic probe manufacturing mold or an X-ray metal grid receiving an X-ray and a method of manufacturing an ultrasonic probe.
Description of the Related Art
For example, an X-ray metal grid which receives an X-ray is used in various devices in the form of an element including a plurality of parallel period structures and is further applied to an X-ray imaging device in recent years. In this X-ray imaging device, X-ray phase imaging has gained attention from the viewpoint of reducing the amount of radiation in recent years. In this case, as the X-ray grid, an absorbing grid which enables or disables the permeation of the X-ray to have a reliable contrast or a phase grid which has a reliable phase difference is needed. In order to realize these grids, a grid having a high aspect ratio structure with a high aspect ratio is needed. For that reason, a manufacturing method using silicon processing adopting a semiconductor processing technique is proposed. For example, WO 2012/008118 A discloses a metal grid manufacturing method. The metal grid manufacturing method disclosed in WO 2012/008118 A is a method of forming a concave portion (a slit) by a dry etching device and burying metal into the concave portion.
However, the dry etching device is expensive. Then, since the expensive dry etching device needs to be used in WO 2012/008118 A, the manufacturing cost increases. Particularly, when a large substrate such as an eight inch or more of a wafer is subjected to dry etching, the manufacturing cost further increases.
In that case, a method of manufacturing a grid by cheaper wet etching is considered. However, when the grid is manufactured by wet etching, a problem arises as below.
For example, when the concave portion is formed by general wet etching, as illustrated in FIGS. 29A and 29B, a portion other than a concave portion forming portion in one principal surface of a substrate 1000 provided with a concave portion is covered by a resist 1001 in accordance with patterning such as photolithography and is immersed into an etching solution 1002 capable of dissolving the substrate 1000 so that a portion not covered by the resist 1001 is dissolved. However, as illustrated in FIG. 29C, when the concave portion is formed at a position adjacent to the resist 1001, the dissolving action of the etching solution 1002 occurs isotropically in general. For this reason, the etching solution flows into the lower surface of the resist 1001 so that undercutting occurs and hence a concave portion 1003 having a side surface inclined with respect to the principal surface is formed. As a result, a problem arises in that a concave portion having a side surface perpendicular to the principal surface is not easily formed.